Contact lenses in wide use today fall into three general categories: hard lenses formed from materials prepared by polymerization of acrylic esters such as poly(methyl methacrylate) (PMMA); rigid gas permeable (RGP) lenses formed from silicone (meth)acrylates and fluorosilicone methacrylates; and gel, hydrogel or like soft-type lenses. The hard and rigid-type lenses, because they are characterized by low vapor diffusion and absorb only minor amounts of aqueous fluids, have a lower tendency to bind ingredients used in contact lens care solutions. On the other hand, soft-type lenses have a greater tendency to bind active ingredients used in contact lens care solutions. Therefore, developing solutions designed for the treatment of soft-type lenses, whether made from the more traditional copolymers of 2-hydroxyethyl methacrylate (HEMA) or from the newer siloxane-containing hydrogel materials is especially challenging.
In the normal course of wearing contact lenses, tear film and debris consisting of proteinaceous, oily, sebaceous, and related organic matter have a tendency to deposit and build-up on lens surfaces. Many factors influence deposit formation, including patient to patient variation, lens material, care regimen, and environment. In general, relatively high water content ionic lens materials absorb more protein than relatively low water content or nonionic lens materials. As part of the routine care regimen, contact lenses must be cleaned to remove tear film deposits and debris. If deposits are not properly removed, both the wettability and optical clarity of the lenses are substantially reduced and wearer discomfort may result.
Further, contact lenses must also be disinfected to kill harmful microorganisms that may be present or grow on the lenses. Some of the most popular products for disinfecting lenses are multi-purpose solutions that can be used to clean, disinfect, and wet contact lenses, followed by direct insertion or placement on the eye, without rinsing. Obviously, the ability to use a single solution for contact lens care is an advantage. Such a solution, however, must be particularly gentle to the eye, since at least some of the solution will be on the lens when inserted or placed on the eye and will thereby come into direct contact with eye tissues.
British Patent Number 1,432,345 discloses contact lens disinfecting compositions containing a polymeric biguanide and a mixed phosphate buffer. Compositions as disclosed by this patent, however, have corneal staining values of 17 percent or more, far above that which is desirable for patient acceptability.
U.S. Pat. No. 6,143,244 discloses a method for treating contact lenses and compositions for such use. The method includes the use of an aqueous biguanide-containing disinfecting solution including an improved buffer system comprising a mixture of a phosphate and a borate buffer. Preferred embodiments of the invention include methods and compositions for simultaneously cleaning and disinfecting contact lenses.
U.S. Pat. No. 4,758,595 discloses a contact lens solution containing a poly(aminopropyl biguanide) (PAPB), also known as poly(hexamethylene biguanide) (PHMB), having enhanced efficacy when combined with a borate buffer. These disinfecting and preservative solutions are especially noteworthy for their broad spectrum of bactericidal and fungicidal activity at low concentrations coupled with very low toxicity when used with soft-type contact lenses. Compositions containing PHMB and borate have been commercialized in various products including multi-purpose solutions, at levels of about 1 ppm or less for use with soft contact lenses.
The fact that multipurpose solutions are designed for use as a wetting agent, without rinsing, means that the solution must be ophthalmically safe for eye contact. This limits, to some extent the type and concentration of both cleaning agents and antimicrobial agents or biocides that can be employed in the solution. For example, as can be readily understood, biocides or cleaners in a shampoo product may not be suitable for ophthalmic use. A challenge has been to develop a formula that is, on the one hand, maximally efficacious and, on the other hand, sufficiently gentle to be not only safe, but comfortable for in-the-eye use.
With conventional contact lens cleaners or disinfectants, including multipurpose solutions, lens wearers typically need to digitally or manually rub the contact lenses, typically between a finger and palm or between fingers, during treatment of the contact lenses. The necessity for the daily “rubbing” of contact lenses adds to the time and effort involved in the daily care of contact lenses. Many contact lens wearers dislike having to perform such a regimen or consider it to be an inconvenience. Some wearers may be negligent in the proper “rubbing” regimen, which may result in contact lens discomfort and other problems. Sometimes rubbing, if performed too rigorously, which is particularly apt to occur with beginning lens wearers, may damage the lenses. This can be problematic when a replacement lens is not immediately available. Some wearers may be negligent in the proper “rinsing” regimen, which may result in contact lens discomfort and other problems.
Contact lens solutions that qualify as a “Chemical Disinfecting Solution” do not require rubbing to meet biocidal performance criteria for destroying representative bacteria and fungi as established by the U.S. Food and Drug Administration (FDA) under the Premarket Notification (510K) Guidance Document for Contact Lens Care Products, May 1, 1997. In contrast, contact lens solutions that qualify as a “Chemical Disinfecting System” do require a rubbing regimen to pass biocidal performance criteria. Traditionally, multipurpose solutions used for disinfecting and wetting or for disinfecting, cleaning and wetting qualify as Chemical Disinfecting Systems, but not as Chemical Disinfecting Solutions.
Traditional contact lens solutions may depend on the rubbing regimen, not only for efficacious disinfection, but also for efficacious cleaning. Thus, in order to develop a contact lens care solution that would provide efficacious cleaning without a rubbing or rinsing regimen, as opposed to “rub and rinse” and/or “no rub with rinse” regimens for cleaning, would require improved cleaning efficacy while still being sufficiently gentle for in-the-eye use.
It would be desirable to obtain a multipurpose contact lens solution that would provide increased cleaning efficacy. It would likewise be desirable to obtain improved cleaning efficacy while maintaining both biocidal efficacy of the solution and low order toxicity of the solution to eye tissue. Desirable solution low order toxicity to eye tissue is such that after the solution is used to treat a contact lens, the lens can be subsequently placed on the eye without rinsing the solution from the lens. While still more challenging to develop, it would also be desirable to obtain a solution that exhibits both efficacious cleaning and disinfection of a contact lens, without requiring a rubbing or rinsing regimen, or at least not inherently or invariably requiring rubbing and rinsing for acceptable performance. Such solution would allow direct placement of the contact lens on an eye following soaking in the solution and/or rinsing and rewetting with the solution.